NHK has reported that tsunami waves may have already reached Iwate Prefecture following the magnitude 7.4 earthquake that struck off the Sanriku coast at 13:23 JST on Monday, April 20. Japan’s Meteorological Agency has issued a full tsunami warning for Iwate Prefecture and Hokkaido’s central Pacific coast with estimated wave heights of up to 3 metres, while tsunami advisories covering 1-metre waves are in effect for Miyagi, Fukushima, eastern and western Hokkaido and Aomori’s Sea of Japan coast.
Authorities are urging all residents in affected coastal areas to evacuate immediately to higher ground without waiting for visual confirmation of waves. The warning is explicit — waves can arrive earlier than forecast, can be significantly higher than estimated, and will hit repeatedly.
Tsunami Warning Zones — 3 Metre Waves Expected
The most serious warnings covering estimated 3-metre wave heights cover three zones. Iwate Prefecture’s tsunami warning states waves may have already reached the coast — with the Miyako observation point estimated arrival at 13:40 JST, Kamaishi at 13:40 JST and Ofunato and Kuji Port at 13:50 JST. All of these times have now passed, meaning waves are actively arriving or have arrived on Iwate’s coastline.
Aomori Prefecture’s Pacific coast faces estimated 3-metre waves, with Mutsuogawara Port’s estimated arrival at 13:50 JST, Hachinohe Port at 14:00 JST and Mutsu City’s Sekinehama at 14:10 JST. Hokkaido’s central Pacific coast faces an estimated 3-metre wave arriving at 14:00 JST at Urakawa Town and Erimo Town’s Shono, and at 14:10 JST at Tokachi Port.
Tsunami Advisory Zones — 1 Metre Waves
Tsunami advisories covering estimated 1-metre wave heights are in effect for Miyagi Prefecture with waves estimated to arrive at Ishinomaki’s Ayukawa at 14:10 JST and Sendai Port at 14:40 JST. Fukushima Prefecture faces advisory-level waves arriving at Onahama around 14:30 JST and Soma at 14:40 JST. Hokkaido’s eastern and western Pacific coasts face advisory-level waves arriving across multiple observation points between 14:00 and 14:40 JST. Aomori’s Sea of Japan coast faces a 1-metre advisory with arrival at Tappi estimated at 14:30 JST.
Why This Is Extremely Serious
The Sanriku coast of Iwate Prefecture is the same stretch of Pacific-facing coastline devastated by the March 11, 2011 Tohoku earthquake and tsunami — the catastrophe that killed nearly 20,000 people and triggered the Fukushima Daiichi nuclear disaster. The deeply indented ria coastline geography of Iwate means that tsunami waves funnel into bays and inlets and amplify dramatically — a 3-metre open-ocean estimate can translate into significantly higher run-up heights when the wave reaches the shore.
The earthquake’s focal depth of just 10 kilometres — extraordinarily shallow — maximises both surface shaking intensity and tsunami generation efficiency. The combination of a 7.4 magnitude event at 10km depth off Sanriku is precisely the seismic profile that Japanese emergency planners treat with the highest urgency. The fact that NHK is already reporting the tsunami may have reached Iwate means the warning window for that coastline is closing or has closed.
Official Warning Message From Japan Meteorological Agency
The JMA’s official advisory text is unambiguous: “Tsunami waves are approaching the coasts. Evacuate as quickly as possible. Waves can hit repeatedly. Continue to evacuate until all warnings are lifted.” The agency has additionally cautioned that “waves can get much higher than expected” — a direct reference to the 2011 experience where initial wave height estimates proved dramatically lower than actual run-up heights at many locations.
The coincidence of tsunami arrival times with local high tide times at several observation points — including Miyako where high tide is at 14:49 JST, Kamaishi and Ofunato where high tide is at 14:53 JST — is a compounding risk factor. Tsunamis arriving near high tide have a higher base water level to build upon, increasing inundation depth and inland penetration.
India and Global Monitoring
The Indian Ocean Tsunami Warning and Mitigation System is monitoring the event as standard protocol. Japan-origin Pacific earthquakes do not typically generate significant Indian Ocean tsunamis given the geographic configuration of landmasses, but monitoring continues across all Indian Ocean coastal nations as a precaution.
For Indian financial markets, a major earthquake and active tsunami in Japan — the world’s third-largest economy and a key technology and automotive supply chain partner — will add to the already complex risk environment heading into Monday’s session, which is also processing the Iran war ceasefire deadline, Trump’s infrastructure threat against Iran and the Vance Pakistan talks announcement.
Business Upturn is monitoring this developing situation continuously. Updates will be issued as wave measurements, damage assessments and casualty information are confirmed by NHK and Japanese authorities.
If you are in an affected coastal area in Japan — evacuate immediately to high ground. Do not wait for visual confirmation of waves. Do not return until all warnings are officially lifted.
Disclaimer: This article is based on NHK reports and Japan Meteorological Agency data. The situation is developing rapidly and all figures are subject to revision by official Japanese authorities.